But before getting settled into the Oval Office, the 57-year-old actor recently sat down at a Dunkin’ Donuts in Harvard Square to discuss making the transition from the critically acclaimed AMC drama to the historical drama onstage here. (And Cranston is that kind of guy. The one without a publicist in tow, perfectly happy to chat over coffee in a Dunkin’ Donuts — decaf, black, no sugar — and get in a little people-watching while he’s at it. His only concession to fame, as the shop fills up, is to slowly edge his chair to face the wall.)

Although he has extensive theater credits, he acknowledges “I am nervous about this. I’m taking a big bite here and leaping into an arena that is not my comfort zone.”

More than just a history lesson about the man who assumed the presidency after John F. Kennedy’s assassination, “All the Way” is an absorbing dramatization of Johnson’s life and his leadership of a turbulent nation in the year between the assassination in November 1963 and Johnson’s election in November 1964.

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Written by Pulitzer Prize-winning playwright Robert Schenkkan (‘The Kentucky Cycle”) and directed by Bill Rauch — reuniting the pair who worked on the show’s world premiere at the Oregon Shakespeare Festival last summer — the play bears witness to what was happening in the White House, in J. Edgar Hoover’s office at the FBI, in the corridors of Congress, and in the headquarters of the Southern Christian Leadership Conference, led by Martin Luther King Jr. As Johnson dealt with war, civil unrest, and eventually the campaign to be elected in his own right, he was working to achieve something other than a tragic promotion to presidency: the passing of the Civil Rights Act in 1964.

With 17 actors playing 35 parts, “All the Way” is a major undertaking. This seems fitting since Johnson was a big man with a big personality.

“What I found out from doing research is that he had a different persona than he presented himself in public,” says Cranston, who agrees this duality of character is something with which he is familiar after playing Walter White for six years.

Cranston recalls thinking of Johnson as stern, taciturn. “But behind the curtain he’s a back-slapper, crude, fun, vicious, engaging, funny, desperate, paranoid, depressed. Reading more and more about him and people who really knew him, they said take all the adjectives in the English language and they all apply to Lyndon Johnson, he’s everything,” says Cranston, clearly relishing the thought of breathing life into those adjectives. “He could be so caring and concerned and then he could be cold as ice. You never know what Johnson you’re going to get.”

For a character with such dimension, director Rauch and playwright Schenkkan wanted a very specific kind of actor, and both are big “Breaking Bad” fans.

“We thought: Who has not just the charisma to pull off LBJ, but the courage and the skill and the heart and the cojones?” says Rauch. “Bryan was obviously a really thrilling choice, and Robert and I were able to meet with him in his home. And to our unbelievable joy, he said yes!”

Colm O’Molloy for The Globe

From left: “All the Way” director Bill Rauch, playwright Robert Schenkkan, and Bryan Cranston, who stars as President Lyndon Johnson.

Cranston says he couldn’t turn it down, and after his wife read the script, she agreed. “You have to,” she told him.

“I have this unbelievable opportunity to throw myself into something that is important, valuable, entertaining, frightening, all of it,” he says. “And that’s not just the play, that’s me. I’m feeling all those things, the character’s feeling all those things, nervousness, and anxiety.” When it’s suggested that some audience members may also be nervous on his behalf, rooting for him to take them on a new journey, he nods. “Expectations are there for sure, and these are all things Lyndon was feeling in the White House.”

It was only after Cranston took the job that the difficulty of the role began to sink in — just how much the part would call for, from memorization to characterization to abrupt tone shifts. “The character is like King Lear, but he’s onstage a hell of a lot more than King Lear is onstage,” says Cranston. “The task ahead is enormous and extremely demanding.”

And he is taking those demands very seriously. He has been in town a few weeks for rehearsal and says he’s only turned on the TV twice, to watch “Breaking Bad.” Otherwise, “I’m tackling this rehearsal period just like Lyndon would, and it’s just like that, an attack. I’ve been very disciplined on how much time I spend on it, what I’m eating. I’m not drinking any alcohol or caffeine. Only one day a week am I allowing myself any carbohydrates to speak of. What’s important is my stamina and my ability to do eight shows a week and keep my voice in gear, and so I needed and wanted a system that would support that and [make] my body the healthiest it can be.”

In addition to reading extensively about Johnson’s life and presidency, he’s also exploring Johnson’s physicality, mannerisms, and accent through audiotapes. And when he lapses into the character to make a point — leaning over the table and intoning in a husky drawl, “He talks like this and he’ll bend his head and he’ll get right into your face! Now how do you like that?” — you can actually see the character emerge.

Says Rauch, “He’s such a transformative actor that his face looks more and more like LBJ’s face to me.”

Technically it is Cranston’s day off but besides some laundry and shopping, he will have his nose in the script.

All of this discipline seems necessary because in “All the Way,” Cranston is the one who talks. And talks, and talks, and talks.

The play requires him to show both the public and private face of the 36th president, and as such he has reams of dialogue to learn. When a reporter wonders how he is going to remember all of these words, Cranston giggles and says, “I keep thinking the same thing!”

Yoichi Okamoto/LBJ Presidential Library via AP

LBJ with Martin Luther King Jr. (left), Whitney Young, and James Farmer in 1964.

The giggle, which is frequent, easy, and accompanied by a happy crinkling around his eyes, makes it seem clear that if there was a time that Walter White haunted Cranston, a new ghost is helping to usher out the old.

“As far as me appearing in a television series again, it’s going to be a few years before I’d even consider something. There has been interest, and I’m grateful for that. But that’s why I wanted to do this play. I needed to step away from that. Walter White was a fantastic role and I’m so blessed to have been able to play him, and he’s indelible, to me and to fans. He’s becoming this iconic figure, and I really have to step away from that and let him go so I can move on.”

For fans who have been stunned by recent events on the show, Cranston laughs and intones mock-ominously, “It gets worse before it gets worser.”

Given the dissecting that happens in the wake of the finales of marquee television shows, Cranston is surprisingly calm regarding fan reaction to what becomes of the man who transformed himself from a milquetoast chemistry teacher to a terrifying drug kingpin.

“I never go online and read those things,” he says. “The idea of reading more about me? I’ve got better things to do. Especially now, I’ve got work to do.”

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